Automatic door openers in common use for applications such as garage doors are subject to several problems which this invention addresses. The principal difficulty in sliding door applications of remotely-actuated power door openers is that the door closure is not completely secure because of system slack and lack of an integral positive lock. This problem is accentuated with modern one-piece, swing arm, spring-biased garage doors which, because they are made in one piece, are not completely rigid, and a determined intruder can gain access by bending up a garage door by its corner even though the closing mechanism remains in the down position. Thus, a more positive perimeter latch system is needed to prevent flexing the door. Although other devices in the art have provided such latching mechanisms, such as Reamey, Door Operating Device, U.S. Pat. No. 2,703,235, sectional door systems such as Reamey cannot be conveniently or effectively integrated with modern one-piece garage door systems.
The within invention provides a delay latching mechanism that can be more effectively and conveniently applied to modern one-piece garage door systems by improving the rigidity of the closure linkage while at the same time maintaining a shock-cushioning mechanism and sufficient delay to enable latch actuation before commencement of door travel. Another problem encountered in installation of modern garage door openers is that for safety reasons modern openers typically include an obstruction sensor and reverse trip switch which may be critically sensitive and affected by addition of other subsystems and functions that could trigger the trip switch. Therefore, the desirable rigidity of the system must be tempered or damped to avoid shocks or to insulate the trip switch from shocks within normal operation while maintaining sufficient tension on the system linkage to continue operation. Finally, since many thousands of door opener installations already exist to which these improvements can or should be applied, the provisions for meeting the above objectives of security and shock insulation should be amenable to retroactive installation, minimizing inconvenience and expense.
These objectives are addressed by the within invention by provision for a linkage of at least two parts movable relative to each other over a short range and spring biased to provide both sufficient tension and shock absorption to the system in operation. The linkage is designed and calculated to easily replace existing rigid linkages and typical door opener installations.
The typical modern one-piece overhead garage door is assembled and adjusted on site by construction contractors who are primarily concerned with keeping costs down. The door is usually made of fiber board or plywood braced by timbers; it is mounted on swing arm carriage, in balance or counter-weighted by adjusting heavy springs to the individual requirements of each door. The varying weights and distances in each door make individual adjustment necessary; a small change in the distance between components can change the lever arm disproportionately and make the door much easier or harder to move. These doors are prone to unpredictable warpage and other changes with age and weather, because they are generally hastily built from various types of low grade wood. Doors that work perfectly one day may swell shut the next. For these reasons, any system added to this sort of door must function effectively over a wide variety of conditions, and a wide range of specifications, and yet have some self-adjusting features.